Semiconductor devices are electronic components used today in virtually all electronic devices and applications. One common semiconductor device is the metal-oxide-semiconductor field-effect transistor (MOSFET). In a MOSFET, a voltage applied to a gate terminal of the device can induce a conducting channel between two other terminals known as the source and drain. A MOSFET essentially functions as a switch which is opened (i.e., turned off) and closed (i.e., turned on) depending on a signal applied to the gate terminal of the device. The MOSFET structure causes the device to turn on/off at a faster rate when a higher voltage level is applied to the gate terminal.
The gate drive requirements for a MOSFET vary according to a number of factors. Process variations, temperature, load conditions, or other factors may all affect the speed at which the MOSFET turns on/off. For example, at cold temperatures, a MOSFET will be able to switch faster than it can at warmer temperatures. The faster switching at cold temperatures can cause problems such as overshoot and ringing in the drain source voltage (VDS) of the MOSFET. Overshoot occurs when the voltage at the switched node exceeds the target voltage due to ringing, where the actual voltage oscillates above and below the target voltage before eventually settling at the target voltage. This effect is seen most often due to parasitic effects. Both effects are undesirable in electronic circuits. The effects of overshoot and ringing decrease at higher temperatures and at lower drive strength due to slower switching, however, the slower switching speeds lead to less efficiency.
The voltage signal applied to the gate terminal is typically generated by a gate driver circuit. Traditionally, the gate driver circuit was configured to apply a gate drive strength such that ringing does not cause voltage ratings of the MOSFET to be exceeded. For example, if the MOSFET is rated at 36 volts (V), and the supply voltage is 30V, then the gate driver circuit may only drive the MOSFET hard enough that 6V of ringing is seen, since any more will cause a voltage rating of the MOSFET to be exceeded. Since the gate drive strength is fixed, the same drive strength is used at higher temperatures even though the overshoot may be less. The drive strength may be set, for example, by using a fixed value resistor placed between an output of a gate driver and the gate terminal of the MOSFET. The lower drive strength to account for overshoot at cold temperatures leads to slower switching and the resulting inefficiency at the higher temperatures.